Polypeptides with phase transition, triblock polypeptides of the polypeptide-calmodulin-polypeptide with multi-stimuli responsiveness, hydrogel of the triblock polypeptides, and its uses

ABSTRACT

Disclosed is a polypeptide having a phase transition behavior, wherein the polypeptide consists of a Val-Pro-Gly-Xaa-Gly (SEQ ID NO: 1) pentapeptide repeat or a Val-Pro-Ala-Xaa-Gly (SEQ ID NO: 2) pentapeptide repeat, and the polypeptide includes a [Val-Pro-Gly-Xaa-Gly (SEQ ID NO: 1)]n or a [Val-Pro-Ala-Xaa-Gly (SEQ ID NO: 1)]n pentapeptide repeat. In addition, the present invention provides a multi-stimuli polypeptide composed of polypeptide-calmodulin-polypeptide having a phase transition behavior and a hydrogel prepared using the same. A dynamic protein hydrogel according to the present invention may be used as a drug carrier, as a scaffold for tissue engineering or as a kit for tissue or organ regeneration.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean Patent Application No. 2016-0030238, filed on Mar. 14, 2016, the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND 1. Field of the Invention

The present invention relates to a novel polypeptide having a phase transition behavior, a triblock polypeptide composed of the polypeptides and calmodulin (i.e., polypeptide-calmodulin-polypeptide) and having multi-stimuli responsiveness, and a hydrogel prepared using the triblock polypeptide. More particularly, the present invention relates to a novel thermally responsive elastin-based polypeptide (EBP), and a newly prepared triblock polypeptide based thereon. In addition, since the hydrogel of the present invention has dynamic properties causing a three-dimensional structural change, the dynamic hydrogel may be used in drug delivery systems, tissue engineering and regenerative medicine.

2. Description of Related Art

Stimuli-responsive protein-based biomaterials which exhibit a three-dimensional hydrogel network induced by sol-gel transition have been of great interest for a variety of biomedical applications because the biomaterials have unique characteristics including stimuli-triggered self-assembly, specific biological functions as well as controllable mechanical properties when hydrogelation occurs. In particular, when conformational changes in the biomaterials occur in response to environmental conditions such as temperature, pH, ionic strength and a ligand, protein hydrogels may undergo three dimensional changes. In this case, the protein hydrogels are called “dynamic hydrogels”. Recently, genetically engineered protein-based materials have been developed as advanced biomaterials for drug delivery, tissue engineering and regenerative medicine applications because the materials have unique amino acid sequences derived from the original proteins of living organisms, monodisperse molecular weights designed at the gene level, excellent biocompatibility with low cytotoxicity, and adjustable biodegradability. Accordingly, a series of elastin, collagen, silk, resilin, calmodulin, metalloproteins, block polypeptides thereof and fusion proteins with biologically active moieties, to be used in preparation of various protein hydrogels for biomedical applications, have been reported.

The elastin-based polypeptides (EBPs) with a repeat unit of a pentapeptide, Val-Pro-(Gly or Ala)-X_(aa)-Gly (SEQ ID NO: 43), where X_(aa) may be any amino acid other than Pro, have been studied because of the controllable environmental responsiveness thereof.

In general, there is a difficulty in applying chemically cross-linked EBP hydrogels to in vivo injectable systems due to cytotoxicity of reaction byproducts and reaction dynamics.

Therefore, the present inventors have continued to study elastin-based proteins that are formed by physical and chemical crosslinking at the same time and have dynamic properties. As a result, the present inventors have developed a novel elastin-based polypeptide, and based on the same, have completed preparation of a multi-stimuli responsive protein-based hydrogel suitable for biomaterial injection.

SUMMARY OF THE INVENTION

Therefore, the present invention has been made in view of the above problems, and it is an objective of the present invention to provide a novel polypeptide having a phase transition behavior.

It is another objective of the present invention to provide a novel triblock polypeptide including the polypeptide block.

It is still another objective of the present invention to provide a dynamic protein hydrogel prepared using the triblock polypeptide.

It is yet another objective of the present invention to provide a composition for drug delivery including the hydrogel.

It is yet another objective of the present invention to provide a scaffold for tissue engineering including the hydrogel.

It is yet another objective of the present invention to provide a kit for tissue or organ regeneration including the hydrogel.

In accordance with the present invention, the above and other objectives can be accomplished by the provision of a polypeptide below:

the polypeptide having a phase transition behavior,

wherein the polypeptide consists of a Val-Pro-Gly-Xaa-Gly (SEQ ID NO:1) pentapeptide repeat or a Val-Pro-Ala-Xaa-Gly (SEQ ID NO:2) pentapeptide repeat, and wherein the polypeptide consists of an amino acid sequence represented by Formula 1 or 2 below and:

Formula 1 [Val-Pro-Gly-Xaa-Gly (SEQ ID NO: 1)]n; or Formula 2 [Val-Pro-Ala-Xaa-Gly (SEQ ID NO: 2)]n, wherein

n is an integer of 2 or more, and is the number of repeats of the pentapeptide; and

Xaa is an amino acid other than proline, and is selected from any natural or artificial amino acid when the pentapeptide VPGXG (SEQ ID NO: 1) or VPAXG (SEQ ID NO: 2) is repeated.

The term “amino acid” used in the present invention refers to a natural or artificial amino acid, preferably a natural amino acid. For example, the amino acid includes glycine, alanine, serine, valine, leucine, isoleucine, methionine, glutamine, asparagine, cysteine, histidine, phenylalanine, arginine, tyrosine, tryptophan and the like.

As used herein, abbreviations such as Gly (G) and Ala (A) are amino acid abbreviations. Gly is an abbreviation for glycine, and Ala is an abbreviation for alanine. In addition, glycine is represented by G and alanine by A. The abbreviations are widely used in the art.

The term “polypeptide” used herein refers to any polymer chain composed of amino acids. The terms “peptide” and “protein” may be used interchangeably with the term polypeptide, and also refer to a polymer chain composed of amino acids. The term “polypeptide” includes natural or synthetic proteins, protein fragments and polypeptide analogs having protein sequences. A polypeptide may be a monomer or polymer.

The term “phase transition” refers to a change in the state of a material, such as when water turns into water vapor or ice turns into water.

The polypeptide according to the present invention is basically a stimuli-responsive elastin-based polypeptide (EBP). The “elastin-based polypeptide” is also called “elastin-like polypeptide (ELP)”, and is a term widely used in the technical field of the present invention.

In the present specification, X (or X_(aa)) is referred to as “guest residue”. Various types of EBPs according to the present invention may be prepared by variously introducing X_(aa).

EBPs undergo a reversible phase transition at a lower critical solution temperature (LCST), also referred to as a transition temperature (T_(t)). EBPs are highly water-soluble below T_(t), but become insoluble when temperature exceeds T_(t).

In the present invention, the physicochemical properties of EBPs are mainly controlled by the combination of a pentapeptide repeat unit, Val-Pro-(Gly or Ala)-X_(aa)-Gly [VP (G or A)XG] (SEQ ID NO: 43). Specifically, the third amino acid of the repeat unit is responsible for determining the relative mechanical properties of EBPs. For example, according to the present invention, the third amino acid Gly is responsible for determining elasticity, or Ala is responsible for determining plasticity. Elasticity and plasticity are properties that appear after a transition occurs.

In addition, the hydrophobicity of a guest residue X_(aa), the fourth amino acid, and multimerization of a pentapeptide repeat unit all affect T_(t).

An EBP according to the present invention may be a polypeptide composed of pentapeptide repeats, and a polypeptide block, i.e., EBP block, may be formed when the polypeptide is repeated. Specifically, a hydrophilic or hydrophobic EBP block may be formed.

The hydrophilic or hydrophobic properties of an EBP block according to the present invention are closely related to the transition temperature of the EBP. The transition temperature of the EBP is also determined by the amino acid sequence of the EBP and molecular weight thereof. A number of studies on the relationship between EBP sequence and T_(t) have been conducted by Urry et al (see Urry D. W., Luan C.-H., Parker T. M., Gowda D. C., Parasad K. U., Reid M. C., and Safavy A. 1991. TEMPERATURE OF POLYPEPTIDE INVERSE TEMPERATURE TRANSITION DEPENDS ON MEAN RESIDUE HYDROPHOBICITY. J. Am. Chem. Soc. 113: 4346-4348). According to the above reference, when, in a pentapeptide of Val-Pro-Gly-Val-Gly (SEQ ID NO: 44), the fourth amino acid, a “guest residue”, is replaced with a residue that is more hydrophilic than Val, T_(t) is increased compared to the original sequence. On the other hand, when the guest residue is replaced with a residue that is more hydrophobic than Val, T_(t) is decreased compared to the original sequence. That is, it was found that a hydrophilic EBP has a high T_(t) and a hydrophobic EBP has a relatively low T_(t). Based on these findings, it has become possible to prepare an EBP having a specific T_(t) by determining which amino acid is used as the guest residue of an EBP sequence and changing the composition ratio of the guest residue (see PROTEIN-PROTEIN INTERACTIONS: A MOLECULAR CLONING MANUAL, 2002, Cold Spring Harbor Laboratory Press, Chapter 18. pp. 329-343).

As described above, an EBP exhibits hydrophilicity when the EBP has a high T_(t), and hydrophobicity when the EBP has a low T_(t). Similarly, in the case of an EBP block according to the present invention, it is also possible to increase or decrease T_(t) by changing an amino acid sequence including a guest residue and molecular weight. Thus, a hydrophilic or hydrophobic EBP block may be prepared.

For reference, an EBP having a T_(t) lower than a body temperature may be used as a hydrophobic block, whereas an EBP having a T_(t) higher than a body temperature may be used as a hydrophilic block. Due to this property of EBPs, the hydrophilic and hydrophobic properties of EBPs may be relatively defined when EBPs are applied to biotechnology.

Taking the sequence of an EBP of the present invention as an example, when a plastic polypeptide block in which a plastic pentapeptide of Val-Pro-Ala-X_(aa)-Gly (SEQ ID NO: 2) is repeated is compared with an elastic polypeptide block in which an elastic pentapeptide of Val-Pro-Gly-X_(aa)-Gly (SEQ ID NO: 1) is repeated, the third amino acid, Gly, has higher hydrophilicity than Ala. Accordingly, the plastic polypeptide block (elastin-based polypeptide with plasticity: EBPP) exhibits a lower T_(t) than the elastic polypeptide block (elastin-based polypeptide with elasticity: EBPE).

EBPs according to the present invention, as described above, may exhibit hydrophilic or hydrophobic properties by adjusting T_(t). In addition, as described below, in physical cross-linking (due to hydrophobic interactions) formed at or above the T_(t) of a hydrophobic EBP, a structural change due to binding between the calcium of CalM and a ligand dynamically changes the three-dimensional structure of a hydrogel.

The polypeptide may have multi-stimuli responsiveness.

The term “multi-stimuli responsiveness” refers to responsiveness to one or more stimuli. Specifically, the stimuli may be one or more selected from the group including temperature, pH, ionic strength and a ligand.

In the present invention, a ligand is a substance that specifically binds to a target substance, and includes, for example, various antibodies, antigens, enzymes, substrates, receptors, peptides, DNA, RNA, aptamers, protein A, protein G, avidin, biotin, chelate compounds, and various metal ions (e.g., calcium ions).

In the present invention, the ligand may be calcium ions and/or a drug, but is not limited thereto.

In one embodiment, the present invention may include the following polypeptides:

[Val-Pro-Gly-Xaa-Gly]6 (SEQ ID NO: 45), that is, the pentapeptide repeats are 6 times, [VPGXG VPGXG VPGXG VPGXG VPGXG VPGXG (SEQ ID NO: 45)], and

each Xaa of the pentapeptide repeats is consisted of A (Ala), G (Gly), and I (Ile) in a ratio of 1:4:1 [SEQ ID NO. 20];

each Xaa of the pentapeptide repeats is consisted of K (Lys), G (Gly), and I (Ile) in a ratio of 1:4:1 [SEQ ID NO. 22];

each Xaa of the pentapeptide repeats is consisted of D (Asp), G (Gly), and I (Ile) in a ratio of 1:4:1 [SEQ ID NO. 24];

each Xaa of the pentapeptide repeats is consisted of E (Glu), G (Gly), and I (Ile) in a ratio of 1:4:1 [SEQ ID NO. 26]; or

each Xaa of the pentapeptide repeats is consisted of G (Gly), A (Ala), and F (Phe) in a ratio of 1:3:2 [SEQ ID NO. 28].

The ratio refers to the amino acid composition of X_(aa) in the pentapeptide repeats.

Specifically, a nucleotide sequence corresponding to the polypeptide may be SEQ ID NO. 3 (a sequence corresponding to SEQ ID NO. 20), SEQ ID NO. 5 (a sequence corresponding to SEQ ID NO. 22), SEQ ID NO. 7 (a sequence corresponding to SEQ ID NO. 24), SEQ ID NO. 9 (a sequence corresponding to SEQ ID NO. 26) or SEQ ID NO. 11 (a sequence corresponding to SEQ ID NO. 28).

In another embodiment, the present invention may include the following polypeptides:

[Val-Pro-Ala-Xaa-Gly]6 (SEQ ID NO: 40), that is, the pentapeptide repeats are 6 times, [VPAXG VPAXG VPAXG VPAXG VPAXG VPAXG (SEQ ID NO: 40)], and

each Xaa of the pentapeptide repeats is consisted of A (Ala), G (Gly), and I (Ile) in a ratio of 1:4:1 [SEQ ID NO. 21];

each Xaa of the pentapeptide repeats is consisted of K (Lys), G (Gly), and I (Ile) in a ratio of 1:4:1 [SEQ ID NO. 23];

each Xaa of the pentapeptide repeats is consisted of D (Asp), G (Gly), and I (Ile) in a ratio of 1:4:1 [SEQ ID NO. 25];

each Xaa of the pentapeptide repeats is consisted of E (Glu), G (Gly), and I (Ile) in a ratio of 1:4:1 [SEQ ID NO. 27];

each Xaa of the pentapeptide repeats is consisted of G (Gly), A (Ala), and F (Phe) in a ratio of 1:3:2 [SEQ ID NO. 29];

each Xaa of the pentapeptide repeats is consisted of K (Lys), A (Ala), and F (Phe) in a ratio of 1:3:2 [SEQ ID NO. 30];

each Xaa of the pentapeptide repeats is consisted of D (Asp), A (Ala), and F (Phe) in a ratio of 1:3:2 [SEQ ID NO. 31];

each Xaa of the pentapeptide repeats is consisted of K (Lys) and F (Phe) in a ratio of 3:3 [SEQ ID NO. 32];

each Xaa of the pentapeptide repeats is consisted of D (Asp) and F (Phe) in a ratio of 3:3 [SEQ ID NO. 33];

each Xaa of the pentapeptide repeats is consisted of H (His), A (Ala), and I (Ile) in a ratio of 3:2:1 [SEQ ID NO. 34];

each Xaa of the pentapeptide repeats is consisted of H (His) and G (Gly) in a ratio of 5:1 [SEQ ID NO. 35]; or

each Xaa of the pentapeptide repeats is consisted of G (Gly), C (Cys), and F (Phe) in a ratio of 1:3:2 [SEQ ID NO. 36].

A nucleotide sequence corresponding to the polypeptide may be SEQ ID NO. 4 (corresponding to SEQ ID NO. 21), SEQ ID NO. 6 (corresponding to SEQ ID NO. 23), SEQ ID NO. 8 (corresponding to SEQ ID NO. 25), SEQ ID NO. 10 (corresponding to SEQ ID NO. 27), SEQ ID NO. 12 (corresponding to SEQ ID NO. 29), SEQ ID NO. 13 (corresponding to SEQ ID NO. 30), SEQ ID NO. 14 (corresponding to SEQ ID NO. 31), SEQ ID NO. 15 (corresponding to SEQ ID NO. 32), SEQ ID NO. 16 (corresponding to SEQ ID NO. 33), SEQ ID NO. 17 (corresponding to SEQ ID NO. 34), SEQ ID NO. 18 (corresponding to SEQ ID NO. 35) or SEQ ID NO. 19 (corresponding to SEQ ID NO. 36).

In accordance with an aspect of the present invention, the above and other objectives can be accomplished by the provision of a triblock polypeptide having multi-stimuli responsiveness, wherein the triblock polypeptide includes of,

a calmodulin block; and

polypeptide blocks having a phase transition behavior linked to both ends of the calmodulin block, and is represented by Formula 3 below: [hydrophobic EBP]m-CalM-[hydrophobic EBP]m, wherein  Formula 3

the [hydrophobic EBP]m refers to a polypeptide block having a phase transition behavior; and the hydrophobic EBP is consisted of a hydrophobic polypeptide selected from the above-described polypeptides having a phase transition behavior;

m is an integer of 2 or more, and is the number of repeats of the hydrophobic polypeptide having a phase transition behavior; and

the CalM is a calmodulin block.

In another embodiment, the present invention may provide a triblock polypeptide having multi-stimuli responsiveness, wherein a polypeptide block having a phase transition behavior further includes a [hydrophilic EBP] linked between the calmodulin block and the [hydrophobic EBP]m of Formula 3, and is represented by Formula 4: [hydrophobic EBP]m-[hydrophilic EBP]x-CalM-[hydrophilic EBP]x-[hydrophobic EBP]m, wherein  Formula 4

the [hydrophobic EBP]m-[hydrophilic EBP]x and [hydrophilic EBP]x-[hydrophobic EBP]m refer to a polypeptide blocks having a phase transition behavior; and

the hydrophobic EBP is consisted of a hydrophobic polypeptide selected from the above-described polypeptides having a phase transition behavior; and the hydrophilic EBP is consisted of a hydrophilic selected from the above-described polypeptides having a phase transition behavior; and;

m or x, each respectively, is an integer of 2 or more, and is the number of repeats of the hydrophobic polypeptide and hydrophilic polypeptide having a phase transition behavior; and

the CalM is a calmodulin block.

A triblock polypeptide according to the present invention is an ABA-type triblock polypeptide. Triblock polypeptides in Formulas 3 and 4 are schematically shown in FIGS. 5A and 5B, respectively.

In EBP blocks constituting the triblock polypeptide and exhibiting a phase transition behavior, a hydrophobic EBP has a lower transition temperature than a hydrophilic EBP. An EBP is insoluble at or above a transition temperature (T_(t) or LSCT). An ABA-type triblock polypeptide according to the present invention forms a physically cross-linked hydrogel by hydrophobic interactions due to the structural change of a hydrophobic EBP under physiological conditions at or above the T_(t) of the hydrophobic EBP. In addition, the present invention may also control rheological and mechanical properties by introducing hydrophilic EBPs.

Since a transition temperature is changed by surrounding environmental conditions such as protein concentration, ionic strength and pH, the transition temperature is determined not as an absolute value but as a relative value. The present invention is related to the aspect of bioengineering. Accordingly, when the transition temperature of an EBP is lower than a body temperature, a triblock polypeptide according to the present invention exhibits hydrophobicity, whereas, when the transition temperature of an EBP is higher than a body temperature, the triblock polypeptide exhibits hydrophilicity. Thus, in the present invention, the hydrophilic and hydrophobic properties of an EBP may be relatively defined when the EBP is used in bioengineering. FIG. 4(F) is an example of an EBP according to the present invention exhibiting hydrophobicity. FIG. 4 shows that other EBPs exhibit hydrophilicity and the transition temperatures of the EBPs are varied under different ionic strength conditions.

In addition, since the calmodulin block has ligand responsiveness, conformational changes may occur when the calmodulin block binds to calcium ions and drugs. In addition, the conformational changes may be caused by dityrosine cross-linking formed by cross-linking of tyrosine residues within the calmodulin block. In addition, once the ligand is removed from the calmodulin, the original conformation of the calmodulin protein may be restored.

The calmodulin block refers to a block composed of calmodulin protein. Since the protein sequence of the calmodulin is already known in the art, any known calmodulin sequence may be used without limitation.

In addition, it is also within the scope of the present invention to use a modified calmodulin that has a partially modified sequence. In an embodiment of the present invention, GAG, a codon corresponding to Glu-83 of calmodulin, was mutated to GAA and the modified calmodulin was used (SEQ ID NO. 38).

In accordance with another aspect of the present invention, there is provided a triblock polypeptide having multi-stimuli responsiveness, wherein the triblock polypeptide includes of:

a calmodulin block; and

polypeptide blocks having a phase transition behavior linked to both ends of the calmodulin block; and

cysteine blocks linked to the polypeptide blocks, and is represented by Formula 5 below: C-[hydrophobic EBP]m-CalM-[hydrophobic EBP]m-C, wherein  Formula 5

in Formula 5,

C is a cysteine block;

the [hydrophobic EBP]m refers to a polypeptide block having a phase transition behavior; and the hydrophobic EBP is consisted of a hydrophobic polypeptide selected from the above-described polypeptides having a phase transition behavior;

m is an integer of 2 or more, and is the number of repeats of the hydrophobic polypeptide having a phase transition behavior; and

the CalM is a calmodulin block.

In another embodiment, the present invention may provide a triblock polypeptide having multi-stimuli responsiveness, wherein a polypeptide block having a phase transition behavior further includes a [hydrophilic EBP]m linked between the calmodulin block and the [hydrophobic EBP]m of Formula 5, and is represented by Formula 6 below: C-[hydrophobic EBP]m-[hydrophilic EBP]x-CalM-[hydrophilic EBP]x-[hydrophobic EBP]m-C, wherein  Formula 6

in Formula 6,

C is a cysteine block;

the [hydrophobic EBP]m-[hydrophilic EBP]x and -[hydrophilic EBP]x-[hydrophobic EBP]m refers to a polypeptide block having a phase transition behavior; and

the hydrophobic EBP is consisted of a hydrophobic polypeptide selected from the above-described polypeptides having a phase transition behavior; and the hydrophilic EBP is consisted of a hydrophilic polypeptide selected from the above-described polypeptides having a phase transition behavior; and;

m or x, each respectively, is an integer of 2 or more, and is the number of repeats of the hydrophobic polypeptide and hydrophilic polypeptide having a phase transition behavior; and

the CalM is a calmodulin block.

The cysteine block refers to a peptide sequence including cysteine. Specifically, the cysteine block may be composed of an amino acid sequence, in which (Gly-Ala-Cys) is repeated one or more times. More specifically, the cysteine block may include a peptide sequence composed of (Gly-Ala-Cys)n [n indicates the number of repetitions], but is not necessarily limited thereto.

In one embodiment of the present invention, a cysteine block having an amino acid sequence, Gly-Ala-Cys-Gly-Ala-Cys-Gly-Ala-Cys-Gly-Ala-Cys, which corresponds to [SEQ ID NO. 39], was used.

Triblock polypeptides in Formulas 5 and 6 are schematically shown in FIGS. 5C and 5D, respectively. EBP blocks having different molecular weights and different T_(t)s are arranged on both sides of a CalM block, and Cys blocks are introduced at both ends of the EBP blocks for chemical cross-linking.

As already described above, since EBP-CalM-EBP triblock polypeptides may reversibly exhibit thermally-triggered gelation, physical cross-linking of hydrophobic EBPs occurs under physiological conditions at or above T_(t), resulting in formation of a physically cross-linked protein hydrogel. In addition, since a calmodulin block has ligand responsiveness, conformational changes may occur when the calmodulin block binds to calcium ions and/or a drug.

The stimuli are as described above. For example, the stimulus may be temperature or a ligand, but is not limited thereto.

In the triblock polypeptide, the polypeptide block having a phase transition behavior may exhibit thermal responsiveness, and the calmodulin block may exhibit ligand responsiveness.

According to one embodiment of the present invention, in the triblock polypeptide having multi-stimuli responsiveness, the [hydrophobic EBP]m may include of an amino acid sequence below:

[hydrophobic EBP]m, m is multiple of six, and

the [hydrophobic EBP] is consisted of an amino acid sequence below:

Val-Pro-Ala-Xaa-Gly [SEQ ID NO. 40], wherein

each Xaa of the pentapeptide repeats is consisted of G (Gly), A (Ala), and F (Phe) in a ratio of 1:3:2.

m may be 6, 12, 18, 24, 30 or 36, but is not limited thereto.

The [hydrophobic EBP]m is described in detail in the following embodiments (see Tables 1 and 2).

In another aspect of the present invention, depending on the unique combination of the pentapeptide repeats, various EBPs and block polypeptides thereof, which have unique physicochemical properties and T_(t)s, were prepared for stimuli-triggered micelle formation and hydrogelation.

Specifically, a hydrogel was prepared by a process including the following steps:

a step of applying a heat stimulus to a triblock polypeptide according to the present invention; and

a step of cross-linking the hydrophobic EBPs of the triblock polypeptide by the heat stimulus and forming a hydrogel.

In another embodiment, the present invention may further include the following steps:

after the hydrophobic EBPs are cross-linked,

a step of inducing a structural change of the calmodulin by specifically binding the calmodulin block, which constitutes the triblock polypeptide, to a ligand; and

a step of forming a dynamic hydrogel by a three-dimensional structural change of the hydrogel induced by the structural change of the calmodulin block due to the ligand responsiveness.

In the step of cross-linking the hydrophobic EBPs, the cross-linking may be physical cross-linking that occurs at or above the transition temperature of the hydrophobic EBP.

In addition, the hydrogel may be formed by dityrosine cross-linking, which is generated by chemically cross-linking tyrosine residues within a calmodulin block constituting the triblock peptide.

In accordance with another aspect of the present invention, there is provided a hydrogel, wherein the hydrogel is prepared by the following process including:

a step of applying a heat stimulus to a triblock polypeptide according to Formula 5 or 6 below;

a step of cross-linking hydrophobic EBPs constituting the triblock polypeptide by the heat stimulus and forming a hydrogel; and a step of chemically cross-linking cysteine blocks constituting the triblock polypeptide. C-[hydrophobic EBP]m-CalM-[hydrophobic EBP]m-C, or  Formula 5 C-[hydrophobic EBP]m-[hydrophilic EBP]x-CalM-[hydrophilic EBP]x-[hydrophobic EBP]m-C,  Formula 6

Since description of Formulas 5 and 6 is the same as that described above, a detailed description thereof is omitted.

The stimuli are as described above. Specifically, the stimuli may be selected from the group consisting of temperature, pH, ionic strength and a ligand, but are necessarily limited thereto, and may be temperature and/or a ligand.

The term “hydrogel” according to the present invention generally refers to a material having a three-dimensional hydrophilic polymer network that may contain a large amount of water. The hydrogel is thermodynamically stable after swelling in an aqueous solution and has mechanical/physicochemical properties corresponding to an intermediate form of liquid and solid.

The hydrogel may be formed by cross-linking the thiol groups of cysteines within cysteine blocks constituting the triblock peptide.

The hydrogel may be formed by dityrosine cross-linking, which is generated by cross-linking tyrosine residues within a calmodulin block constituting the triblock peptide. Specifically, in one embodiment of the present invention, it was demonstrated that the tyrosine residues of the calmodulin block may be chemically cross-linked to form dityrosines via UV irradiation.

ABA-type EBP-CalM-EBP triblock polypeptides according to the present invention exhibit multi-stimuli responsiveness to temperature, calcium, and drug molecules, forming a dynamic protein hydrogel that is triggered by multi-stimuli. In addition, these dynamic protein hydrogels are useful in injectable drug delivery systems, functional tissue engineering, and regenerative medicine.

A triblock polypeptide according to the present invention is prepared by linking polypeptide blocks having thermal responsiveness and a calmodulin block having ligand responsiveness. Thus, in the triblock polypeptide according to the present invention, physical cross-linking may be formed at a temperature at or above the temperature corresponding to the biological environment, i.e., a temperature at or above T_(t). In addition, in the triblock polypeptide, chemical crosslinking and physical crosslinking may occur simultaneously. In addition, the triblock polypeptide has calcium and ligand responsiveness. Therefore, a hydrogel using the triblock polypeptide according to the present invention has dynamic properties, and is a protein-based dynamic hydrogel that is a suitable injectable biomaterial and has stimuli-responsiveness.

In EBPs according to the present invention, physical cross-linking and chemical cross-linking occur at the same time. A variety of physically cross-linked EBP hydrogels have been developed for use as injectable biomaterials for drug delivery and storage, scaffolds for tissue engineering, and fillers for regenerative medicine. ABA-type triblock EBPs composed of a plastic EBP block having a low T_(t) and an elastic EBP block having a high T_(t) form physically cross-linked hydrogels at or above the low T_(t) due to hydrophobic interactions between aggregated plastic EBP blocks. In addition, when triblock polypeptides including repeats of a plastic pentapeptide, Val-Pro-Ala-X_(aa)-Gly (SEQ ID NO: 2), were self-assembled via thermal transition, the triblock polypeptides exhibited higher mechanical properties than triblock polypeptides including repeats of an elastic pentapeptide, Val-Pro-Gly-X_(aa)-Gly (SEQ ID NO: 1). These physically cross-linked EBP triblocks may be applied to in vivo injectable systems. The present inventors also studied chemically cross-linked EBP hydrogels using various strategies including oxidation-reduction, UV or gamma irradiation, and covalent linkage via multi-functional linkers and enzymes. Since these chemically cross-linked EBP hydrogels exhibited improved mechanical properties over the physically cross-linked EBP hydrogels, the chemically cross-linked EBP hydrogels may be applied to cartilage tissue repair and vascular grafting.

The term “dynamic hydrogel’ has the following meaning. A substance (e.g., protein) constituting a hydrogel may undergo a conformational change in response to a specific environmental condition, such as temperature, pH, ionic strength, and a ligand. In this case, the gel is called a “dynamic hydrogel”.

Ligand binding-triggered conformational changes of proteins may be used to develop dynamic protein-based hydrogels because protein conformation changed by a ligand may be converted back to the natural conformation upon ligand removal. Specifically, calmodulin (CalM) with relative molecular mass of 17,000, a multi-functional intermediate messenger protein, is a calcium-binding protein including four high-affinity Ca²⁺ binding sites with a K_(d) (dissociation constant) in a range of 0.1 to 1 mM. When calcium ions bind to four helix-loop-helix motifs of CalM, the CalM protein undergoes a large conformational change, resulting in formation of dumbbell shaped structures at both ends of a long central helix. Furthermore, as the CalM associates with CalM-dependent proteins in the Ca²⁺-bound state, the central helix of the CalM is warped. Likewise, the CalM in the Ca²⁺-bound state undergoes a conformational change in the presence of certain ligand molecules such as phenothiazine derivatives and chlorpromazine. Finally, metal chelators including ethylenediaminetetraacetic acid (EDTA) and ethylene glycol-bis(β-aminoethyl ether)-N, N, N′, N′-tetraacetic acid (EGTA) may remove all Ca²⁺ and ligands bound to the CalM, and as a result, the CalM may return to the original state thereof.

As can be seen from the present invention, a three-dimensional change of a hydrogel occurs due to a dramatic conformational change in CalM, which is induced by Ca²⁺ and a ligand bound to a CalM or removal of the Ca²⁺ and ligand by metal chelators.

In accordance with another aspect of the present invention, there is provided a composition for drug delivery including the hydrogel.

Since the hydrogel responds to a ligand, a drug may be introduced into the hydrogel and be stably transferred to the body.

In accordance with another aspect of the present invention, there is provided a scaffold for tissue engineering including the hydrogel.

The scaffold for tissue engineering according to the present invention includes all scaffolds that may be used in the field of tissue engineering for the purpose of maintaining, enhancing or restoring the function of the body by preparing and implanting substitutes for living tissues.

In accordance with still another aspect of the present invention, there is provided a kit for tissue or organ regeneration including the hydrogel.

In the kit for tissue or organ regeneration according to the present invention, in addition to the scaffold for tissue engineering, a reinforcing layer for maintaining the shape of the scaffold may be added. The reinforcing layer may be selected from biodegradable polymer materials such as PCL, PLA, PLGA, and PGA.

The present invention provides a new class of dynamic protein hydrogels composed of genetically engineered ABA-type EBP-CalM-EBP triblock polypeptides.

In the following embodiments, a series of an ABA-type triblock polypeptide composed of multi-stimuli responsive elastin-based polypeptides (EBPs) and a ligand-responsive calmodulin (CalM) were genetically designed, expressed, and purified by inverse transition cycling (ITC) and based on the triblock polypeptides, multi-stimuli responsive dynamic protein hydrogels were prepared. For example, an EBP sequence with a pentapeptide repeat unit of Val-Pro-(Gly or Ala)-X_(aa)-Gly (SEQ ID NO: 43) was designed at the DNA level so that the fourth residue represented Gly, Ala, and Phe in a molar ratio of 1:3:2 and the T_(t) at or below the physiological temperature was optimized. EBP blocks with amino acid composition ratios of X_(aa) of pentapeptides which are differently repeated were arranged on both sides of a CalM block, and Cys blocks which are chemically cross-linkable domains were introduced at both ends of the EBP blocks. The EBP-CalM-EBP triblock polypeptides exhibited reversible thermally-triggered gelation, and based on this, physically crosslinked protein hydrogels were obtained at or above T_(t) under physiological conditions, as characterized by rheological measurements. Furthermore, the physically crosslinked hydrogels of the EBP-CalM-EBP triblock polypeptides exhibited responsiveness to ligands for a CalM block, such as calcium and phenothiazine, a drug (ligand). Therefore, EBP-CalM-EBP triblock polypeptides exhibit multi-stimuli responsiveness to temperature, calcium, and ligand molecules, forming dynamic protein hydrogels that are triggered by the multi-stimuli. Potentially, these dynamic protein hydrogels may be useful in injectable drug delivery systems, functional tissue engineering, and regenerative medicine.

Stimuli-responsive protein-based biomaterials have been of great interest in the biomedical field because of stimuli-triggered self-assembly, superior biocompatibility, superior mechanical properties and specific biological functions thereof. In the following embodiments, a series of an ABA-type triblock polypeptide composed of thermally responsive elastin-based polypeptide blocks and a ligand-responsive calmodulin block were genetically designed, expressed, and purified by inverse transition cycling (ITC) and based on the triblock polypeptides, multi-stimuli responsive dynamic protein hydrogels were prepared. The EBP-CalM-EBP triblock polypeptides exhibited reversible thermally-triggered gelation, and as shown by rheological measurements, physically cross-linked protein hydrogels were formed above a transition temperature under physiological conditions. Furthermore, the physically crosslinked hydrogels of the EBP-CalM-EBP triblock polypeptides exhibited responsiveness to ligands for a CalM block, such as calcium and phenothiazine.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objectives, features and advantages of the present invention will become more apparent to those of ordinary skill in the art by describing exemplary embodiments thereof in detail with reference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram showing construction of plasmids encoding EBP gene libraries with different DNA sizes and block polypeptides thereof. A modified vector was designed to include restriction sites recognized by three different restriction enzymes (REs), including XbaI (RE1), AcuI (RE2), and BseRI (RE3). For example, a gene construct encoding EBPP[G₁A₃F₂]₁₂ was prepared by a ligation reaction, in which a plasmid backbone and an insert derived from a plasmid-borne gene vector harboring a gene encoding EBPP[G₁A₃F₂]₆ were used: The plasmid-borne gene vector harboring a gene encoding EBPP[G₁A₃F₂]₆ was double-digested by XbaI and AcuI to obtain an insert, i.e., a gene fragment encoding EBPP[G₁A₃F₂]₆. On the other hand, the plasmid-borne gene vector for EBPP[G₁A₃F₂]₆ was double-digested by XbaI and BseRI to obtain a plasmid backbone and then the plasmid backbone was dephosphorylated by treatment with alkaline phosphatase;

FIG. 2 shows agarose gel electrophoresis images of EBP gene libraries according to the present invention. (A) EBPE[A₁G₄I₁], (B) EBPP[A₁G₄I₁], (C) EBPE[K₁G₄I₁], (D) EBPP[K₁G₄I₁], (E) EBPE[D₁G₄I₁], (F) EBPP[D₁G₄I₁], (G) EBPE[E₁G₄I₁], (H) EBPP[E₁G₄I₁], (I) EBPP[G₁A₃F₂], (J) EBPP[K₁A₃F₂], (K) EBPP[D₁A₃F₂], and (L) EBPP[H₃A₂I₁]. The number of EBP repeat units is indicated below each DNA band. The bilateral lanes on all agarose gels represent different DNA size markers (0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 1.0, 1.5, 2.0, and 3.0 kbp, from bottom to top);

FIG. 3 shows copper-stained SDS-PAGE gel (4 to 20% gradient) images of EBPs according to the present invention. (A) EBPE[A₁G₄I₁], (B) EBPP[A₁G₄I₁], (C) EBPE[K₁G₄I₁], (D) EBPP[K₁G₄I₁], (E) EBPE[D₁G₄I₁] and (F) EBPP[D₁G₄I₁]. Two-sided lanes on the SDS-PAGE gels contain standard protein size markers (7, 15, 24, 35, 40, 50, 65, 90, 110, and 150 kDa, from bottom to top);

FIG. 4 shows the thermal profiles of EBPs according to the present invention. (A) EBPE[A₁G₄I₁]_(n), (B) EBPP[A₁G₄I₁]_(n), (C) EBPE[K₁G₄I₁]_(n), (D) EBPP[K₁G₄]_(n), (E) EBPP[D₁G₄I₁]_(n) and (F) EBPP[G₁A₃F₂]_(n). To obtain thermal profiles, 25 μM EBP solutions were prepared in PBS buffer or PBS buffer supplemented with 1 to 3 M NaCl, and optical absorbance of the EBP solutions was measured at 350 nm while heating the solutions at a heating rate of 1° C./min;

FIG. 5 shows schematic diagrams of dynamic protein hydrogels composed of genetically engineered ABA-type EBP-CalM-EBP triblock polypeptides. Two different types of EBP blocks, such as a hydrophobic EBP having a low T_(t) and a hydrophilic EBP having a high T_(t), were introduced. (A) hydrophobic EBP-CalM-hydrophobic EBP, (B) hydrophobic EBP-hydrophilic EBP-CalM-hydrophilic EBP-hydrophobic EBP, (C) Cys block-hydrophobic EBP-CalM-hydrophobic EBP-Cys block, and (D) Cys block-hydrophobic EBP-hydrophilic EBP-CalM-hydrophilic EBP-hydrophobic EBP-Cys block;

FIG. 6 shows the DNA agarose gel electrophoresis (0.8%) images (left) and the copper-stained SDS-PAGE (4-20% gradient) gel images (right) of a series of constructed Cys-EBPP[G₁A₃F₂]_(6n)-CalM-EBPP[G₁A₃F₂]_(6n)-Cys (n: integer). Each lane of the gel on either side represents (1) Cys block-EBPP[G₁A₃F₂]₆-CalM-EBPP[G₁A₃F₂]₆-Cys block, (2) Cys block-EBPP[G₁A₃F₂]₁₂-CalM-EBPP[G₁A₃F₂]₁₂-Cys block, (3) Cys block-EBPP[G₁A₃F₂]₁₈-CalM-EBPP[G₁A₃F₂]₁₈-Cys block, (4) Cys block-EBPP[G₁A₃F₂]₂₄-CalM-EBPP[G₁A₃F₂]₂₄-Cys block, (5) Cys block-EBPP[G₁A₃F₂]₃₀-CalM-EBPP[G₁A₃F₂]₃₀-Cys block, and (6) Cys block-EBPP[G₁A₃F₂]₃₆-CalM-EBPP[G₁A₃F₂]₃₆-Cys block;

FIG. 7 shows the thermal profiles of Cys block-EBPP[G₁A₃F₂]_(6n)-CalM-EBPP[G₁A₃F₂]_(6n)-Cys block in 10 mM HEPES buffer at pH 7.4 (A) and in 10 mM HEPES buffer supplemented with 10 mM CaCl₂ (B), when characterized by turbidity profiling as a function of temperature at a heating rate of 1° C./min. Each number in (A) and (B) represents (1) Cys block-EBPP[G₁A₃F₂]₆-CalM-EBPP[G₁A₃F₂]₆-Cys block, (2) Cys block-EBPP[G₁A₃F₂]₁₂-CalM-EBPP[G₁A₃F₂]₁₂-Cys block, (3) Cys block-EBPP[G₁A₃F₂]₁₈-CalM-EBPP[G₁A₃F₂]₁₈-Cys block, (4) Cys block-EBPP[G₁A₃F₂]₂₄-CalM-EBPP[G₁A₃F₂]₂₄-Cys block, (5) Cys block-EBPP[G₁A₃F₂]₃₀-CalM-EBPP[G₁A₃F₂]₃₀-Cys block, and (6) Cys block-EBPP[G₁A₃F₂]₃₆-CalM-EBPP[G₁A₃F₂]₃₆-Cys block;

FIG. 8 shows the images of the reversible sol-gel transition behaviors of Cys block-EBPP[G₁A₃F₂]₁₂-CalM-EBPP[G₁A₃F₂]₁₂-Cys block in 10 mM HEPES buffer at pH 7.4, as a function of temperature, when sequentially incubated at 4° C. (A), 37° C. (B and C), and 4° C. (D);

FIG. 9 shows temperature-dependent rheological behaviors of Cys block-EBPP[G₁A₃F₂]₁₂-CalM-EBPP[G₁A₃F₂]₁₂-Cys block in 10 mM HEPES buffer at pH 7.4 as a function of polypeptide concentration (1 rad/s, 2% shear strain): (A) 16.6 wt. %, (B) 23.1 wt. %, (C) 27.0 wt. %, and (D) 28.6 wt. %. Storage modulus (G′), loss modulus (G″), and loss angle (δ) obtained by measuring each oscillatory shear were plotted as a function of temperature at a heating rate of 1° C./min; and

FIG. 10 shows oscillatory rheological profiles of 27.0 wt. % Cys block-EBPP[G₁A₃F₂]₁₂-CalM-EBPP[G₁A₃F₂]₁₂-Cys block in 10 mM HEPES buffer (A and C) or in 10 mM HEPES buffer containing 168 mM CaCl₂ (B and D), wherein A and B are profiles as a function of temperature at 1 rad/s and 2% shear strain, and C and D are profiles as a function of frequency at 10 or 40° C. and 2% shear strain.

DETAILED DESCRIPTION OF THE INVENTION Example 1: Materials

A pET-21a vector and BL21 (DE3) E. coli cells were obtained from Novagen Inc. (Madison, Wis., U.S.). Top10 competent cells were obtained from Invitrogen (Carlsbad, Calif., U.S.). Oligonucleotides were chemically synthesized in Cosmo Gene Tech (Seoul, South Korea). FastAP, a thermosensitive alkaline phosphatase, and restriction endonucleases including BamHI and XbaI were purchased from Fermentas (Ontario, Canada). Other restriction endonucleases including BseRI, AcuI and other restriction enzymes were obtained from New England Biolabs (Ipswich, Mass., U.S.). T4 DNA ligase was obtained from Elpis Bio-tech (Taejeon, South Korea). All kits for DNA mini-preparation, gel extraction, and PCR purification were obtained from Geneall Biotechnology (Seoul, South Korea). Dyne Agarose High was obtained from DYNE BIO (Seongnam, South Korea). All Top10 cells were grown in TB DRY media (MO BIO Laboratories, Carlsbad, Calif., U.S.) and super optimal broth with catabolite repression (SOC) media (Formedium, UK) was supplemented with 20 mM glucose. All BL21 (DE3) cells were grown in Circlegrow media obtained from MP Biomedicals (Solon, Ohio, U.S.). Ready Gel (Tris-HCl, 2-20%), a precast gel, was obtained from Bio-Rad (Hercules, Calif., U.S.). Phosphate buffered saline (PBS, pH 7.4), ampicillin, polyethyleneimine (PEI), calcium chloride, ethylenediaminetetraacetic acid (EDTA), ethylene glycol-bis(β-aminoethyl ether)-N, N, N′, N′-tetraacetic acid (EGTA), phenothiazine (PTZ), chlorpromazine (CPZ), and trifluoperazine (TFP) were obtained from Sigma-Aldrich (St Louis, Mo.).

Example 2: Notation for Different EBP Blocks and Block Polypeptides Thereof

Different EBPs having a pentapeptide repeat unit of Val-Pro-(Gly or Ala)-X_(aa)-Gly[VP (G or A)XG] (SEQ ID NO: 43) are named as follows. X_(aa) may be any amino acid except Pro. First, pentapeptide repeats of Val-Pro-Ala-X_(aa)-Gly (VPAXG (SEQ ID NO: 2)) with plasticity are defined as an elastin-based polypeptide with plasticity (EBPP). On the other hand, pentapeptide repeats of Val-Pro-Gly-X_(aa)-Gly (VPGXG (SEQ ID NO: 1)) are called an elastin-based polypeptide with elasticity (EBPE). Second, in [X_(i)Y_(j)Z_(k)]_(n), the capital letters in the parentheses represent the single letter amino acid codes of guest residues, i.e., amino acids at the fourth position (X_(aa) or X) of an EBP pentapeptide, and subscripts corresponding to the capital letters indicate the ratio of the guest residues in an EBP monomer gene as a repeat unit. The subscript number n of [X_(i)Y_(j)Z_(k)]_(n) represents the total number of repeats of an EBP. For example, EBPP[G₁A₃F₂]₁₂ is an EBPP block including 12 repeats of the Val-Pro-Gly-X_(aa)-Gly (SEQ ID NO: 1) pentapeptide unit, in which a ratio of Gly, Ala, and Phe at the fourth guest residue position (X_(aa)) is 1:3:2. Finally, the EBP-CalM-EBP triblock polypeptides are named by the composition of each block in square brackets with a hyphen between blocks such as EBPP[G₁A₃F₂]₁₂-CalM-EBPP[G₁A₃F₂]₁₂.

Example 3: Preparation of Modified pET-21a Vector for Cloning Seamless Gene

Four micrograms of a pET-21a vector was digested and dephosphorylated with 50 U of XbaI, 50 U of BamHI and 10 U of a thermosensitive alkaline phosphatase in FastDigest buffer for 20 minutes at 37° C. The restricted plasmid DNA was purified using a PCR purification kit, and then was eluted in 40 μl of distilled and deionized water. Two oligonucleotides with XbaI and BamHI compatible sticky ends were designed, i.e., SEQ ID NO. 40 (5′-ctagaaataattttgtttaactttaagaaggaggagtacatatgggctactgataatgatcttcag-3′) and SEQ ID NO. 41 (5′-gatcctgaagatcattatcagtagcccatatgtactcctccttcttaaagttaaacaaaattattt-3′). To anneal the two types of oligonucleotides, each oligonucleotide was prepared at a concentration of 2 μM in 50 μl of T4 DNA ligase buffer, heat treated at 95° C. for 2 minutes and then slowly cooled to room temperature over 3 hours. To ligate the annealed dsDNA, i.e., a DNA insert, into multiple cloning sites within the linearized pET-21a vector, 20 pmol of the annealed dsDNA and 0.1 pmol of the linearized pET-21a vector were incubated in T4 DNA ligase buffer containing 1 U of T4 DNA ligase for 30 minutes at 37° C. The modified pET-21a (mpET-21a) vector for cloning and expressing a seamless gene was transformed into Top10 competent cells, followed by plating the Top10 competent cells on a super optimal broth with catabolite repression (SOC) plate supplemented with 50 μg/ml of ampicillin. The DNA sequence of the mpET-21a vector was then verified by fluorescent dye terminator DNA sequencing (Applied Biosystems Automatic DNA Sequencer ABI 3730).

Example 4: Synthesis of EBP Monomer Gene and Oligomerization Thereof

The EBP sequences having a pentapeptide repeat unit, Val-Pro-(Gly or Ala)-X_(aa)-Gly (SEQ ID NO: 43), in which the fourth residues were varied in different molar ratios, were designed at the DNA level to optimize T_(t) below a physiological temperature. The DNA and amino acid sequences of EBPs with various pentapeptide repeat units for 17 EBP libraries are shown in Tables 1 and 2, respectively.

TABLE 1 Gene sequences corresponding to EBP libraries. Both EBPs with plasticity (EBPPs) having a pentapeptide repeat of Val-Pro-Ala-X_(aa)-Gly (SEQ ID NO: 2), and EBPs with elasticity (EBPEs) having a pentapeptide repeat of Val-Pro-Gly-X_(aa)-Gly (SEQ ID NO: 1) were all cloned to have the same guest residue composition and ratio. SEQ ID EBP Gene Sequence NO. EBPE[A₁G₄I₁] GTC CCA GGT GGA GGT GTA CCC GGC GCG GGT GTC CCA GGT GGA GGT  3 GTA CCT GGG GGT GGG GTC CCT GGT ATT GGC GTA CCT GGA GGC GGC EBPP[A₁G₄I₁] GTT CCA GCT GGC GGT GTA CCT GCT GCT GCT GTT CCG GCC GGT GGT  4 GTT CCG GCG GGC GGC GTG CCT GCA ATA GGA GTT CCC GCT GGT GGC EBPE[K₁G₄I₁] GTT CCG GGT GGT GGT GTT CCG GGT AAA GGT GTT CCG GGT GGT GGT  5 GTT CCG GGT GGT GGT GGT GTT CCG GGT ATC GGT GTT CCG GGT GGC EBPP[K₁G₄I₁] GTT CCG GCG GGT GGT GTT CCG GCG AAA GGT GTT CCG GCG GGT GGT  6 GTT CCG GCG GGT GGT GTT CCG GCG ATC GGT GTT CCG GCG GGT GGC EBPE[D₁G₄I₁] GTT CCG GGT GGT GGT GTT CCG GGT GAT GGT GTT CCG GGT GGT GGT  7 GTT CCG GGT GGT GGT GGT GTT CCG GGT ATC GGT GTT CCG GGT GGC EBPP[D₁G₄I₁] GTT CCG GCG GGT GGT GTT CCG GCG GAT GGT GTT CCG GCG GGT GGT  8 GTT CCG GCG GGT GGT GTT CCG GCG ATC GGT GTT CCG GCG GGT GGC EBPE[E₁G₄I₁] GTT CCG GGT GGT GGT GTT CCG GGT GAA GGT GTT CCG GGT GGT GGT  9 GTT CCG GGT GGT GGT GGT GTT CCG GGT ATC GGT GTT CCG GGT GGC EBPP[E₁G₄I₁] GTT CCG GCG GGT GGT GTT CCG GCG GAA GGT GTT CCG GCG GGT GGT 10 GTT CCG GCG GGT GGT GTT CCG GCG ATC GGT GTT CCG GCG GGT GGC EBPE[G₁A₃F₂] GTC CCG GGT GCG GGC GTG CCG GGA TTT GGA GTT CCG GGT GCG GGT 11 GTT CCA GGC GGT GGT GTT CCG GGC GCG GGC GTG CCG GGC TTT GGC EBPP[G₁A₃F₂] GTG CCG GCG GCG GGC GTT CCA GCC TTT GGT GTG CCA GCG GCG GGA 12 GTT CCG GCC GGT GGC GTG CCG GCA GCG GGC GTG CCG GCT TTT GGC EBPP[K₁A₃F₂] GTG CCG GCG GCG GGC GTT CCA GCC TTT GGT GTG CCA GCG GCG GGA 13 GTT CCG GCC AAA GGC GTG CCG GCA GCG GGC GTG CCG GCT TTT GGC EBPP[D₁A₃F₂] GTG CCG GCG GCG GGC GTT CCA GCC TTT GGT GTG CCA GCG GCG GGA 14 GTT CCG GCC GAT GGC GTG CCG GCA GCG GGC GTG CCG GCT TTT GGC EBPP[K₃F₃] GTT CCA GCG TTT GGC GTG CCA GCG AAA GGT GTT CCG GCG TTT GGG 15 GTT CCC GCG AAA GGT GTG CCG GCC TTT GGT GTG CCG GCC AAA GGC EBPP[D₃F₃] GTT CCA GCG TTT GGC GTG CCA GCG GAT GGT GTT CCG GCG TTT GGG 16 GTT CCC GCG GAT GGT GTG CCG GCC TTT GGT GTG CCG GCC GAT GGC EBPP[H₃A₃I₁] GTG CCG GCG CAT GGA GTT CCT GCC GCC GGT GTT CCT GCG CAT GGT 17 GTA CCG GCA ATT GGC GTT CCG GCA CAT GGT GTG CCG GCC GCC GGC EBPP[H₅G₁] GTT CCG GCC GGA GGT GTA CCG GCG CAT GGT GTT CCG GCA CAT GGT 18 GTG CCG GCT CAC GGT GTG CCT GCG CAT GGC GTT CCT GCG CAT GGC EBPP[G₁C₃F₂] GTG CCG GCG TGC GGC GTT CCA GCC TTT GGT GTG CCA GCG TGC GGA 19 GTT CCG GCC GGT GGC GTG CCG GCA TGC GGC GTG CCG GCT TTT GGC

TABLE 2 Amino acid sequences corresponding to EBP libraries. SEQ ID EBP Amino acid Sequence NO. EBPE[A₁G₄I₁] VPGGG VPGAG VPGGG VPGGG 20 VPGIG VPGGG EBPP[A₁G₄I₁] VPAGG VPAAG VPAGG VPAGG 21 VPAIG VPAGG EBPE[K₁G₄I₁] VPGGG VPGKG VPGGG VPGGG 22 VPGIG VPGGG EBPP[K₁G₄I₁] VPAGG VPAKG VPAGG VPAGG 23 VPAIG VPAGG EBPE[D₁G₄I₁] VPGGG VPGDG VPGGG VPGGG 24 VPGIG VPGGG EBPP[D₁G₄I₁] VPAGG VPADG VPAGG VPAGG 25 VPAIG VPAGG EBPE[E₁G₄I₁] VPGGG VPGEG VPGGG VPGGG 26 VPGIG VPGGG EBPP[E₁G₄I₁] VPAGG VPAEG VPAGG VPAGG 27 VPAIG VPAGG EBPE[G₁A₃F₂] VPGAG VPGFG VPGAG VPGGG 28 VPGAG VPGFG EBPP[G₁A₃F₂] VPAAG VPAFG VPAAG VPAGG 29 VPAAG VPAFG EBPP[K₁A₃F₂] VPAAG VPAFG VPAAG VPAGG 30 VPAAG VPAFG EBPP[D₁A₃F₂] VPAAG VPAFG VPAAG VPAGG 31 VPAAG VPAFG EBPP[K₃F₃] VPAFG VPAKG VPAFG VPAKG 32 VPAFG VPAKG EBPP[D₃F₃] VPAFG VPADG VPAFG VPADG 33 VPAFG VPADG EBPP[H₃A₃I₁] VPAHG VPAAG VPAHG VPAIG 34 VPAHG VPAAG EBPP[H₅G₁] VPAGG VPAHG VPAHG VPAHG 35 VPAHG VPAHG EBPP[G₁C₃F₂] VPACG VPAFG VPACG VPAGG 36 VPACG VPAFG

In Table 1, SEQ ID NO. 3 to 10 may be classified as gene sequences for hydrophilic EBP blocks, and SEQ ID NO. 11 to 19 may be classified as gene sequences for hydrophobic EBP blocks, in which Phe and His are incorporated. That is, as described above, when the LCST of an EBP is lower than the body temperature, the EBP exhibits hydrophobicity, and when the LCST of an EBP is higher than the body temperature, the EBP exhibits hydrophilicity. Due to this property of EBPs, the hydrophilic and hydrophobic properties of EBPs may be relatively defined when EBPs are applied to biotechnology.

Different EBPs having a pentapeptide repeat unit, Val-Pro-(Gly or Ala)-X_(aa)-Gly (SEQ 10 ID NO: 43) [where X_(aa) may be any amino acid except Pro], which are capable of responding to unique stimuli including temperature and pH, were designed at the DNA level. EBPs with plasticity (EBPPs) having a pentapeptide repeat unit of Val-Pro-Ala-X_(aa)-Gly (SEQ ID NO: 2) and EBPs with elasticity (EBPEs) having a pentapeptide repeat unit of Val-Pro-Gly-X_(aa)-Gly (SEQ ID NO: 1) were all cloned to have the same guest residue composition and ratio. Tables 1 and 2 represent the gene and amino acid sequences of different EBPs having respective pentapeptide repeat units. For example, EBPE[G₁A₃F₂]₁₂ and EBPP[G₁A₃F₂]₁₂ not only show almost the same molar mass, but also the fourth residues of these EBP pentapeptide repeat units represent the same combination. In addition, these EBP blocks have different mechanical properties because the third amino acid residue (Ala or Gly) of the pentapeptide repeat units are different. Positively and negatively charged EBPs were constructed by introducing charged amino acids such as Lys, Asp, Glu, His and the like as guest residues.

To anneal each pair of oligonucleotides encoding various EBPs, each oligonucleotide was prepared at a concentration of 2 μM in 50 μl of T4 DNA ligase buffer, heat treated at 95° C. for 2 minutes and then slowly cooled to room temperature over 3 hours. Four micrograms of a modified pET-21a (mpET-21a) vector was digested and dephosphorylated with 15 U of BseRI and 10 U of FastAP thermosensitive alkaline phosphatase for 30 minutes at 37° C. The restricted plasmid DNA was purified using a PCR purification kit, and then was eluted in 40 μl of distilled and deionized water. To ligate the annealed dsDNA, i.e., a DNA insert, into multiple cloning sites within the linearized mpET-21a vector, 90 pmol of the annealed dsDNA and 30 pmol of the linearized mpET-21a vector were incubated in T4 DNA ligase buffer containing 1 U of T4 DNA ligase for 30 minutes at 16° C. The ligated plasmid was transformed into Top10 chemically competent cells, followed by plating the Top10 competent cells on a SOC plate supplemented with 50 μg/ml of ampicillin. DNA sequences was then verified by DNA sequencing. After all EBP monomer genes were constructed, each EBP gene was synthesized by ligating each of 36 types of repetitive genes (as an insert) into the corresponding vector containing each of the same 36 types of repetitive genes, as follows. A cloning procedure for EBP libraries and fusions thereof is illustrated in FIG. 1. Vectors harboring gene copies corresponding to EBP monomers were digested and dephosphorylated with 10 U of XbaI, 15 U of BseRI and 10 U of FastAP thermosensitive alkaline phosphatase in CutSmart buffer for 30 minutes at 37° C. The restricted plasmid DNA was purified using a PCR purification kit, and then was eluted in 40 μl of distilled and deionized water. For preparation of an insert part, a total of 4 μg of an EBP monomer gene were digested with 10 U of XbaI and 15 U of AcuI in CutSmart buffer for 30 minutes at 37° C. After digestion, the reaction product was separated by agarose gel electrophoresis and the insert was purified using a gel extraction kit. A ligation reaction was performed by incubating 90 pmol of the purified insert with 30 pmol of the linearized vector in T4 DNA ligase buffer containing 1 U of T4 DNA ligase for 30 minutes at 16° C. The product was transformed into Top10 chemically competent cells, then the cells were plated on a SOC plate supplemented with 50 μg/ml of ampicillin. Transformants were initially screened by a diagnostic restriction digest on an agarose gel and further confirmed by DNA sequencing as described above.

As described above, EBP gene libraries having different DNA sizes were synthesized using the designed plasmid vector and three different restriction endonucleases. FIG. 1 illustrates a recursive directional ligation (RDL) method, in which EBP monomer genes are ligated to form oligomerized EBP genes. For example, a gene construct encoding EBPP[G₁A₃F₂]₂ was prepared by a ligation reaction, in which a plasmid backbone and an insert derived from a plasmid-borne gene vector harboring a gene encoding EBPP[G₁A₃F₂]₆ were used: The plasmid-borne gene vector harboring a gene encoding EBPP[G₁A₃F₂]₆ was double-digested by XbaI and AcuI to obtain an insert, i.e., a gene fragment encoding EBPP[G₁A₃F₂]₆. On the other hand, the plasmid-borne gene vector for EBPP[G₁A₃F₂]₆ was double-digested by XbaI and BseRI to obtain a plasmid backbone and then the plasmid backbone was dephosphorylated by treatment with an alkaline phosphatase. The RDL method using two different double restriction enzymes has several advantages. First, due to the different shapes of the protrusions of both an insert and a restricted vector, a self-ligating reaction of the restricted vector did not occur, and the insert and the restricted vector were efficiently linked in a head-tail orientation. Second, due to the mechanism of a type III restriction endonuclease, an additional DNA sequence encoding each linker between blocks is not required. Each EBP gene was oligomerized to generate 36, 72, 108, 144, 180, and 216 EBP pentapeptide repeats. Using two restriction endonucleases Xba I and BamH I, oligomerized gene sizes with 540, 1080, 1620, 2160, 2700, and 3240 base pairs (bps) were confirmed. As characterized by agarose gel electrophoresis, FIG. 2 depicts the restricted DNA bands of EBP libraries with DNA size markers on both end lanes. For example, EBPE[A₁G₄I₁] in FIG. 2(A) clearly shows a restricted DNA band corresponding to a DNA region encoding an oligomerized pentapeptide sequence containing Ala, Gly, Ile in a ratio of 1:4:1 as a guest residue. All of the restricted DNA bands are shown as corresponding lengths as compared to the molecular size markers.

The triblock polypeptides composed of EBP genes and calmodulin were overexpressed in E. coli having a T7 promoter and purified by multiple cycles of inverse transition cycling (ITC). FIG. 3 shows copper-stained SDS-PAGE gel images of the purified EBPs. EBPs shifted at least 20% more than theoretically calculated molecular weights. Two-sided lanes on SDS-PAGE gels contain standard protein size markers (7, 15, 24, 35, 40, 50, 65, 90, 110, and 150 kDa, from bottom to top). In FIGS. 3(A) and 3(B), EBPE[A₁G₄I₁] and EBPP[A₁G₄I₁] represent a series of corresponding proteins with a molecular weight greater than a theoretical molecular weight (in the case of EBPE[A₁G₄I₁], 14.0, 27.7, 41.3, 55.0, and 68.6 kDa, from left to right). In general, as shown in FIGS. 3(C) and 3(D), positively charged EBP libraries, including EBPE[K₁G₄I₁] and EBPP[K₁G₄I₁], showed higher molecular weights than nonpolar EBP libraries, including EBPE[A₁G₄I₁] and EBPP[A₁G₄I₁]. In addition, as shown in FIGS. 3(E) and 3(F), negatively charged EBP libraries, including EBPE[D₁G₄I₁] and EBPP[D₁G₄I₁], have differently charged characteristics, and thus exhibited higher molecular weights than positively charged EBP libraries.

The EBP libraries were characterized. FIG. 4 shows thermal transition behaviors of EBPs determined by measuring optical absorbance at 350 nm (absorbance₃₅₀) at a heating rate of 1° C./min. An inverse transition temperature (T_(t)) is defined as a temperature at which the first derivative (d (OD₃₅₀)/dT) of turbidity, which is a function of temperature, was the maximum. Based on environmental conditions such as salt concentration and pH and the different third and fourth amino acids of an EBP pentapeptide repeat unit, the T_(t) of an EBP was finely controlled in PBS and PBS was supplemented with 1 to 3 M NaCl. For example, EBPE[A₁G₄I₁]₁₂ (FIG. 4(A)) with Gly at the third amino acid of an EBP pentapeptide repeat exhibited a T_(t) about 15° C. higher than that of EBPP[A₁G₄I₁]₁₂ (FIG. 4(B)) with Ala at the third amino acid of an EBP pentapeptide repeat in PBS containing 1 M NaCl, because Gly at the third amino acid of an EBP pentapeptide repeat has higher hydrophilicity than Ala. In general, charged EBP libraries have a higher T_(t) than nonpolar EBP libraries because charged residues were introduced into the fourth amino acid of the EBP pentapeptide repeat of the charged EBPs. Negatively charged EBP libraries, such as EBPP[D₁G₄I₁] (FIG. 4(E)), have different pK_(a) values for Asp and Lys at the fourth amino acid of an EBP pentapeptide repeat, and thus have a higher T_(t) than positively charged EBP libraries, such as EBPE[K₁G₄I₁] (FIG. 4(C)) and EBPP[K₁G₄I₁] (FIG. 4(D)). For reference, (A), (B), (C), (D) and (E) of FIG. 4 represent hydrophilicity, and (F) of FIG. 4 represents hydrophobicity.

Example 5: Gene Design for Block Including Calmodulin and Cys

A CalM gene was derived from Rattus norvegicus CalM 3 (GenBank: BC063187.1). Originally, the gene has two BseRI recognition sites, of which the sequence is GAGGAG. Accordingly, to construct the gene libraries of EBP-CalM-EBP triblock polypeptides by molecular cloning, GAG, a codon corresponding to Glu-83 of CalM, was modified to GAA because GAG and GAA are codons for Glu.

A rationally designed recombinant CalM gene was prepared through a gene synthesis service provided by Invitrogen (Carlsbad, Calif., U.S.), and restricted by XbaI and BseRI to perform seamless ligation for construction of the gene libraries of EBP-CalM-EBP triblock polypeptides. In addition, to perform reversible intermolecular crosslinking by oxidation and reduction as well as drug conjugation for chemotherapeutics, a Cys-incorporated block (Cys block) with multiple Cys residues was designed such that Cys was cyclically located in a repetitive gene sequence, (Gly-Ala-Cys)₄. A pair of oligonucleotides for the Cys-incorporated block were chemically synthesized by Cosmo Genetech (Seoul, Korea) and annealed to a dsDNA fragment including restriction sites for AcuI and BseRI.

As shown in Table 3, a CalM gene derived from Rattus norvegicus CalM 3 was prepared. Since both GAG and GAA are codons for Glu, GAG, a codon corresponding to Glu-83 of CalM, was modified to GAA (the dark colored area in Table 3). Using this modified CalM gene, seamless ligation was performed for construction of the gene libraries of EBP-CalM-EBP triblock polypeptides, which have restriction sites for restriction enzymes including XbaI and BseRI. In addition, to perform reversible intermolecular crosslinking by oxidation and reduction as well as drug conjugation for chemotherapeutics, a Cys-incorporated block (Cys block) with multiple Cys residues was designed at the DNA level such that Cys was cyclically located in a repetitive gene sequence, (Gly-Ala-Cys)₄.

TABLE 3 Gene (SEQ ID NO. 37) and amino acid (SEQ ID NO. 38) sequences of calmodulin (CalM) GCT GAC CAG CTG ACC GAA GAA CAG ATT GCA GAG TTC  A   D   Q   L   T   E   E   Q    I   A   E   F AAG GAA GCC TTC TCC CTC TTT GAC AAG GAT GGA GAT   K   E   A   F   S   L   F  D   K   D   G   D GGC ACC ATT ACC ACC AAG GAG CTG GGG ACT GTG ATG   G   T   I   T   T   K   E   L   G   T   V   M AGA TCG CTG GGG CAA AAC CCC ACT GAG GCG GAA CTG   R   S  L   G   Q   N   P   T    E   A   E   L CAG GAC ATG ATC AAT GAG GTG GAT GCT GAT GGC AAT   Q   D   M   I   N   E   V   D   A  D   G   N GGG ACC ATT GAC TTC CCA GAG TTC CTG ACC ATG ATG  G   T   I    D   F   P   E   F   L   T   M   M GCC AGA AAG ATG AAG GAT ACA GAC AGC GAG GAA GAG   A   R   K   M  K   D   T   D   S   E   E   E ATA CCA GAG GCC TTC CGT GTC TTT GAC AAG GAT GGG   I   P   E   A   F   R   V   F   D   K   D  G AAT GGC TAC ATC AGT GCT GCT GAG CTG CGT CAC GTC  N   G   Y   I    S   A   A   E   L   R   H   V ATG ACG AAC CTG GGG GAG AAG CTG ACT GAT GAG GAA   M   T   N   L   G   E   K   L   T   D   E   E GTG GAT GAG ATG ATC CGA GAG GCG GAC ATT GAT GGA   V   D   E   M   I   R   E   A   D   I   D   G GGC GGC CAG GTC AAT TAT GAA GAG TTT GTA CAG ATG   G  G   Q   V   N   Y   E   E   F   V   Q   M ATG ACT  M   T ※ Area marked in bold is mutated region, and underlined representation is dityrosine binding region

Example 6: Gene Construction of EBP-CalM-EBP Triblock Polypeptide

Each plasmid containing EBP, CalM, or a Cys-incorporated block was used to prepare genes for the fusion polypeptide libraries of EBP[G₁A₃F₂]_(n)-CalM-EBP[G₁A₃F₂]_(n) with Cys blocks at both ends. A plasmid vector harboring an EBP gene was digested and dephosphorylated with 10 U of XbaI, 10 U of BseRI and 10 U of FastAP, a thermosensitive alkaline phosphatase, in CutSmart buffer for 30 minutes at 37° C. The restricted plasmid DNA was purified using a PCR purification kit, and then was eluted in 40 μl of distilled and deionized water. A total of 4 μg of the CalM gene was digested with 10 U of XbaI and 15 U of AcuI in the CutSmart buffer for 30 minutes at 37° C. to prepare the CalM gene as an insert, followed by separation using agarose gel electrophoresis and purification using a gel extraction kit. A ligation reaction was performed by incubating 90 pmol of the purified insert with 30 pmol of the linearized vector in T4 DNA ligase buffer containing 1 U of T4 DNA ligase for 30 minutes at 16° C. The product was transformed into Top10 chemically competent cells, then the cells were plated on a SOC plate supplemented with 50 μg/ml of ampicillin. Transformants were initially screened by a diagnostic restriction digest on an agarose gel and further confirmed by DNA sequencing as described above.

Example 7: Gene Expression and Purification of EBPs and Block Polypeptides Thereof

E. coli strain BL21(DE3) cells were transformed with each vector containing an EBP or EBP block polypeptide, and then inoculated in 50 ml of CircleGrow media supplemented with 50 μg/ml ampicillin. Preculturing was performed in a shaking incubator at 200 rpm overnight at 37° C. 50 ml of CircleGrow media was then inoculated in 500 ml of CircleGrow media with 50 μg/ml ampicillin and incubated in a shaking incubator at 200 rpm for 16 hours at 37° C. When optical density at 600 nm (OD₆₀₀) reached 1.0, overexpression of an EBP gene or a block polypeptide gene thereof was induced by addition of IPTG at a final concentration of 1 mM. The cells were centrifuged at 4500 rpm for 10 minutes at 4° C. The expressed EBPs and block polypeptides thereof were purified by inverse transition cycling (ITC) as reported previously (see Dong Woo Lim, Kimberly Trabbic-Carlson, J. Andrew MacKay and Ashutosh Chilkoti, “IMPROVED NON-CHROMATOGRAPHIC PURIFICATION OF A RECOMBINANT PROTEIN BY CATIONIC ELASTIN-LIKE POLYPEPTIDES”, Biomacromolecules, 8 (5), 1417-1424, 2007). The cell pellet was resuspended in 30 ml of HEPES buffer, and the cells were lysed by sonication for 10 s at 20 s intervals (VC-505, Sonics & Materials Inc, Danbury, Conn.) on an ice bath. The cell lysate was centrifuged in a 50 ml centrifuge tube at 13000 rpm for 15 min at 4° C. to precipitate the insoluble debris of the cell lysate. A supernatant containing water soluble EBPs was then transferred to a new 50 ml centrifuge tube and centrifuged with 0.5% w/v of PEI at 13000 rpm for 15 minutes at 4° C. to precipitate nucleic acid contaminants. The inverse phase transition of the EBPs were triggered by adding sodium chloride at a final concentration of 3 to 4 M, and the aggregated EBPs were separated from the lysate solution by centrifugation at 13000 rpm for 15 minutes at 37° C. The aggregated EBPs were resuspended in cold HEPES buffer, and the EBP solutions were centrifuged at 13000 rpm for 15 minutes at 4° C. to remove any aggregated protein contaminants. These aggregation and resuspension processes were repeated 5 to 10 times until the purity of EBP reached approximately 95%, as determined by SDS-PAGE and gel permeating chromatography with a high-performance liquid chromatography (HPLC) 1260 series instrument (Agilent Technologies, Palo Alto, Calif., USA) using Shodex GPC column OHpak SB-804 HQ (Showa Denko Co., Tokyo, Japan). Deionized water at 20° C. was used as an eluent at a flow rate of 1 ml/min and a GPC column was maintained at 20° C. A low-dispersity pullulan in the range of 5900 to 200000 g/mol was used as a standard. The EBPs and the block copolypeptides thereof were analyzed with a refractive index detector (RID) and a variable wavelength detector (VWD) at 280 nm. An effect of temperature on inverse phase transition of the various EBPs and the block polypeptides thereof at 25 μM concentration in HEPES buffer was determined by measuring OD₃₅₀ using a Cary 100 Bio UV/Vis Spectrophotometer equipped with a multi-cell thermoelectric temperature controller (Varian Instruments, Walnut Creek, Calif.) at 10 to 85° C. at a rate of 1° C./min.

FIG. 5 shows schematic diagrams of dynamic protein hydrogels composed of genetically engineered ABA-type EBP-CalM-EBP triblock polypeptides. Two different types of EBP blocks, such as a hydrophobic EBP having a low T_(t) and a hydrophilic EBP having a high T_(t), were introduced. A series of EBP-CalM-EBP triblock polypeptides in FIG. 5 were designed as follows: (A) hydrophobic EBP-CalM-hydrophobic EBP, (B) hydrophobic EBP-hydrophilic EBP-CalM-hydrophilic EBP-hydrophobic EBP, (C) Cys block-hydrophobic EBP-CalM-hydrophobic EBP-Cys block, and (D) Cys block-hydrophobic EBP-hydrophilic EBP-CalM-hydrophilic EBP-hydrophobic EBP-Cys block. EBP blocks having different molecular weights and different T_(t)s were arranged on both sides of the CalM block, and Cys blocks were introduced at both ends of the EBP blocks for chemical cross-linking. Since EBP-CalM-EBP triblock polypeptides may reversibly exhibit thermally initiated gelation, a physically cross-linked protein hydrogel may be generated under physiological conditions at or above T_(t). In addition, an EBP-CalM-EBP triblock polypeptide may form a physically cross-linked protein hydrogel under aqueous solution conditions above the transition temperature of a hydrophobic EBP, and ligands such as calcium and a phenothiazine drug specifically bind to CalM, thereby inducing a structural change in CalM to dynamically change the three-dimensional network of the hydrogel. Furthermore, the thiol groups of Cys blocks at both ends may be chemically crosslinked via oxidation, and Tyr residues in the CalM block may be also chemically crosslinked into dityrosine via UV irradiation. Depending on multi-responsiveness of the EBP-CalM-EBP triblock polypeptides, physicochemical and mechanical properties thereof may be finely controlled. Consequently, EBP-CalM-EBP triblock polypeptides exhibit multi-stimuli responsiveness to temperature, calcium, and ligand molecules, forming a dynamic protein hydrogel that is triggered by the multi-stimuli.

Example 8: Rheological Measurement of Physically and Chemically Cross-Linked Hydrogels

EBP-CalM-EBP triblock polypeptide solutions were prepared in different HEPES buffers supplemented with various concentrations of oxidizing and reducing agents, CaCl₂, or phenothiazine as ligands for CalM. The EBP-CalM-EBP solutions were studied in dynamic-shear rheological testing (cone-and-plate configuration, cone angle=1.58°, diameter=20 mm, TA DHR1 with Peltier plate, TA instruments, Inc., U.S.) to quantify the elastic modulus (G′), loss modulus (G″), complex shear modulus (G*), complex viscosity (η*), and loss angle (δ) as functions of temperature and frequency. The G′ characterizes the elastic behavior of a material whereas the G″ characterizes the viscous behavior of the material. The G* and η* represent the frequency-dependent stiffness, and the frequency-dependent viscous drag of a viscoelastic liquid or solid, respectively. The loss angle (δ) is a relative measure of viscous to elastic properties (Newtonian viscous fluid: δ=90°; elastic solid: δ=0°). A metal solvent trap under fully hydrating conditions was used to prevent solvent evaporation over temperatures ranging from 10 to 40° C. All samples were equilibrated for at least 5 to 10 minutes at the desired temperatures prior to each experiment. Dynamic frequency sweep measurements were performed in the linear viscoelastic regime at different temperatures, as confirmed by independent strain sweep tests (strain sweep range: 0.2 to 20%, angular frequency: 0.1 or 10 rad/s). The angular frequency ranged from 0.1 to 10 rad/s, both at 10° C. (below T_(t)) and 40° C. (above T_(t)) for the frequency sweep tests.

The temperature sweep tests were executed with 2% strain at 1 rad/s over a temperature range of 10 to 40° C. with one minute in duration per degree for forward heating and reverse cooling measurements to examine the reversibility of rheological and mechanical properties thereof. The storage modulus (G′), the loss modulus (G″), the complex shear modulus (G*), the complex viscosity (η*), and the loss angle (δ) were obtained from each oscillatory shear measurement. Each experiment was performed three times to ensure reproducibility.

Hydrophobic EBPP[G₁A₃F₂] blocks with various molecular weights (M.W.) was introduced into the Cys block-hydrophobic EBP-CalM-hydrophobic EBP-Cys block at the DNA level. A DNA agarose gel electrophoresis image in FIG. 6 (left) clearly shows the different DNA sizes of a series of constructed Cys block-EBPP[G₁A₃F₂]_(6n)-CalM-EBPP[G₁A₃F₂]_(6n)-Cys block (n: integer) in the range of 1596, 2676, 3756, 4836, 5916, and 6996 base pairs (bps) from the first to sixth lane. The triblock polypeptides were overexpressed in E. coli and purified by ITC as described above. A copper-stained SDS-PAGE gel in FIG. 6 (right) shows that these triblock polypeptides were purified to at least 95% homogeneity by five to six rounds of ITC, as characterized by GPC analysis. The theoretical molecular weights of the polypeptides shown on the right of the gel in FIG. 6 (right) are 49.0, 79.1, 109.2, 139.4, 169.5, and 199.6 kDa from the first to sixth lane. It was found that the polypeptides were partly oxidized during SDS-PAGE, indicating dimers formed via disulfide bridges.

FIG. 7 shows the thermal transition behaviors of the polypeptides in the absence (A) or presence (B) of 10 mM CaCl₂ when the polypeptides were characterized by turbidity profiling as a function of temperature at a heating rate of 1° C./min. Depending on different EBPP[G₁A₃F₂] block sizes as a hydrophobic block and calcium binding to the CalM, T_(t)s of the polypeptides were finely controlled in the range from 29.4 to 47.3° C. As the EBPP[G₁A₃F₂] block length increased, the T_(t) of the polypeptides became lower irrespective of calcium binding to the CalM. In particular, when calcium ions were bound to the CalM, the CalM of the triblock polypeptides underwent a large conformational change, forming a dumbbell shaped structure. Therefore, the T_(t) of the polypeptides in the presence of 10 mM CaCl₂ were approximately 1.6 to 6.2° C. lower than those in the absence of calcium ions due to increased hydrophobicity induced by a large conformational change of the CalM. Potentially, the calcium bound CalM structure in the dumbbell shaped structure at both ends of a long central helix may make the distance between EBPP[G₁A₃F₂] blocks within the triblock polypeptides much shorter than that without calcium.

Example 9: Viscoelastic Behavior of EBP-CalM-EBP Triblock Polypeptides

FIG. 8 shows photographic images of reversible sol-gel transition behavior of the Cys block-EBPP[G₁A₃F₂]₁₂-CalM-EBPP[G₁A₃F₂]₁₂-Cys block in 10 mM HEPES buffer at pH 7.4 as a function of temperature. When the EBP-CalM-EBP triblock polypeptide was prepared in HEPES buffer at 27 wt. %, a viscoelastic liquid with viscous flow at 4° C. became a viscoelastic solid at 37° C. due to physical crosslinking between aggregated EBPP blocks within the triblock polypeptide at 37° C. In particular, as shown in FIG. 8(C), the physically cross-linked hydrogel at 37° C. was easily detached from a tube by simply tapping a finger, indicating rheological and mechanical properties of the physically cross-linked hydrogel at 37° C. FIGS. 8(A) to 8(D) show that transition behavior from the viscoelastic solid to the viscoelastic liquid was reversible as temperature decreased from at 37 to 4° C. because of reversible phase transition behavior of an EBPP block as shown in FIGS. 8(A) to 8(D).

FIGS. 9 and 10 show the temperature and ligand-dependent rheological and mechanical properties of the Cys block-EBPP[G₁A₃F₂]₁₂-CalM-EBPP[G₁A₃F₂]₁₂-Cys block in 10 mM HEPES buffer at pH 7.4 as functions of polypeptide concentration and CaCl₂. A series of independent strain sweep tests were performed in the range from 0.2 to 20% at various angular frequencies of 0.1, 1.0 or 10.0 rad/s. Dynamic frequency sweep measurements at 2% strain were performed in the linear viscoelastic regime at different temperatures. The angular frequency ranged from 0.1 to 10 rad/s, both at 10° C. below T_(t) and 40° C. above T_(t) for the dynamic frequency sweep tests. The temperature sweep tests were executed with 2% strain at 1.0 rad/s over a temperature range of 10 to 40° C. with one minute in duration per degree for forward heating and reverse cooling measurements to examine the reversibility of rheological and mechanical properties thereof. The storage modulus (G′), the loss modulus (G″), the complex shear modulus (G*), the complex viscosity (η*), and the loss angle (δ) were obtained from each oscillatory shear measurement. FIG. 9 clearly shows controlled gelation temperature (t), which is defined as a temperature of the crossover point of G′ and G″ in the temperature sweep measurement. As shown in FIG. 9, thermally induced phase transition of the triblock polypeptide in 10 mM HEPES buffer at pH 7.4 occurred at 22 to 23° C. in the concentration range of 16.6-28.6 wt. % and the G′ and G″ values continued to increase due to intra- or intermolecular hydrophobic interactions between the aggregated EBPP blocks within the triblock polypeptide as the temperature increased. In particular, as the temperature increased above the T_(t), the complex shear modulus (G*) values largely increased about 3 orders of magnitude greater than that 10° C. below the T_(t), indicating enhanced stiffness due to the evolved viscoelasticity.

As shown in FIG. 10, an effect of calcium binding to CalM on both thermally induced phase transition and rheological properties of the triblock polypeptide was also characterized by oscillatory rheological measurements when 10 mM HEPES buffer at pH 7.4 was supplemented with 168 mM CaCl₂ to have a 10-fold molar excess of CaCl₂ as compared to the 4.2 mM EF-hand motif of CalM. Thermally induced phase transition of the triblock polypeptide in the presence of calcium (FIG. 10 (B)) occurred at 19° C., which is 3° C. lower than that without calcium (FIG. 10 (A)) because the CalM of the triblock polypeptides underwent a large conformational change, forming into a dumbbell shaped structure when calcium ions were bound to the CalM. Although the complex shear modulus (G*) showed similar values irrespective of calcium binding to CalM, the loss angle (δ) in the presence of calcium was 36°, which was 20° higher than that without calcium. Potentially, when a large conformational change of CalM of the triblock polypeptides was induced by calcium binding, the calcium bound CalM structure in the dumbbell shaped structure at both ends of a long central helix may make the distance between EBPP[G₁A₃F₂] blocks within the triblock polypeptides much shorter than that without calcium, suggesting a lowered viscoelastic solid property. FIGS. 10(C) and 10(D) show the frequency-dependent rheological behavior of the triblock polypeptide without (C) and with (D) calcium binding to CalM at 10 and 40° C. In general, the elastic property at 40° C. dominated over a wide frequency range of 0.1 to 10 rad/s at 2% strain and the values of the complex viscosity (1*) are highly frequency dependent with a 10-fold difference or greater due to a intermolecular physical cross-linking of the aggregated EBPP blocks. This proved that the triblock polypeptide was a physically cross-linked hydrogel in conditions higher than the transition temperature of hydrophobic EBP, and depending on the presence or absence of calcium binding to the CalM, (C) and (D) showed different values of G′, G″ and η* depending on frequency. These indicated that rheologically and mechanically different protein hydrogels were formed.

TABLE 4 Transition temperature of EBP-CalM-EBP triblock polypeptides in the presence of 10 mM CaCl₂ as compared to free calM without CaCl₂. Free CalM CalM with EBP-CalM-EBP library (° C.) Ca²⁺(° C.) A Cys-EBPP[G₁A₃F₂]₆-CalM-EBPP[G₁A₃F₂]₆-Cys 47.3 40.1 B Cys-EBPP[G₁A₃F₂]₁₂-CalM-EBPP[G₁A₃F₂]₁₂-Cys 43.2 36.1 C Cys-EBPP[G₁A₃F₂]₁₈-CalM-EBPP[G₁A₃F₂]₁₈-Cys 37.4 33.5 D Cys-EBPP[G₁A₃F₂]₂₄-CalM-EBPP[G₁A₃F₂]₂₄-Cys 35.0 31.9 E Cys-EBPP[G₁A₃F₂]₃₀-CalM-EBPP[G₁A₃F₂]₃₀-Cys 32.4 30.8 F Cys-EBPP[G₁A₃F₂]₃₆-CalM-EBPP[G₁A₃F₂]₃₆-Cys 29.4 30.7

Transition temperature of EBP-CalM-EBP triblock polypeptides in the presence of 10 mM CaCl₂ as compared to free CalM without CaCl₂.

TABLE 5 Thermal transition temperature (Tt), gelation temperature (τ), complex shear modulus (|G*|) and phase angle (δ) of 27.0 wt. % Cys block-EBPP[G₁A₃F₂]₁₂-CalM-EBPP[G₁A₃F₂]₁₂-Cys block in HEPES and HEPES supplemented with 168 mM CaCl₂ measured by oscillatory rheological profiles at 1 rad/s and 2% shear strain. Solvent T_(t) (° C.) τ (° C.) |G*| (Pa) δ (°) HEPES 20.9 24.1 756.2 15.3 HEPES with 168 mM CaCl₂ 17.4 24.0 404.7 33.8

The EBP-CalM-EBP triblock polypeptide as an ABA-type showed multi-responsiveness to temperature, calcium and ligand molecules at a molecular level. The physically crosslinked hydrogel of the EBP-CalM-EBP triblock polypeptide was formed by thermal and ligand stimuli, and was found to have reversible sol-gel transition behavior. These dynamic hydrogels also showed different rheological and mechanical properties via multi-responsiveness to calcium, and ligand molecules.

Potentially, the physically crosslinked hydrogels may be further chemically crosslinked via disulfide bonds of the Cys blocks via oxidation, and dityrosine of CalM via light. These multi-responsive dynamic protein hydrogels may be used in drug delivery system, tissue engineering, and regenerative medicine.

The hydrogel according to the present invention can be used in injectable drug delivery systems, functional tissue engineering and regenerative medicine. 

What is claimed is:
 1. A triblock polypeptide having multi-stimuli responsiveness, wherein the triblock polypeptide is consisted of a calmodulin block; and polypeptide blocks having a phase transition behavior linked to both ends of the calmodulin block, and is represented by Formula 3 below: [hydrophobic EBP]m-CalM-[hydrophobic EBP]m, wherein  Formula 3 the [hydrophobic EBP]m refers to a polypeptide block having a phase transition behavior; and the hydrophobic EBP is a pentapeptide of Val-Pro-Ala-Xaa-Gly (SEQ ID NO: 2), wherein Xaa is an amino acid other than proline; m is an integer of 2 or more, and is the number of repeats of the hydrophobic polypeptide having a phase transition behavior; and the CalM is a calmodulin block, wherein an amino acid sequence encoding the calmodulin is SEQ ID NO:
 38. 2. The triblock polypeptide according to claim 1, wherein the [hydrophobic EBP]m, m is multiple of six, and the [hydrophobic EBP] is consisted of an amino acid sequence below: Val-Pro-Ala-Xaa-Gly [SEQ ID NO. 40], wherein each Xaa of the pentapeptide repeats is consisted of G (Gly), A (Ala), and F (Phe) in a ratio of 1:3:2.
 3. The triblock polypeptide according to claim 2, wherein m is 6, 12, 18, 24, 30 or
 36. 4. A hydrogel, wherein the hydrogel is prepared by a process comprising: applying a heat stimulus to the triblock polypeptide according to claim 1; and cross-linking hydrophobic EBPs of the triblock polypeptide by the heat stimulus and forming a hydrogel.
 5. The hydrogel according to claim 4, wherein the hydrogel is prepared by a process comprising: after the hydrophobic EBPs are cross-linked, inducing a structural change of the calmodulin by specifically binding the calmodulin block, which constitutes the triblock polypeptide, to a ligand; and forming a dynamic hydrogel by a three-dimensional structural change of the hydrogel induced by the structural change of the calmodulin block due to the ligand responsiveness.
 6. The hydrogel according to claim 4, wherein, in the cross-linking, the cross-linking is physical cross-linking that occurs at or above a transition temperature of the hydrophobic EBP.
 7. The hydrogel according to claim 5, wherein the ligand is calcium and/or a drug.
 8. The hydrogel according to claim 4, wherein the hydrogel is formed by dityrosine cross-linking, which is generated by chemically cross-linking tyrosine residues within a calmodulin block constituting the triblock peptide.
 9. A composition for drug delivery comprising the hydrogel according to claim
 4. 10. A scaffold for tissue engineering comprising the hydrogel according to claim
 4. 11. A kit for tissue or organ regeneration comprising the hydrogel according to claim
 4. 